1. Field of the Invention
The present invention relates to an optical transceiver.
2. Related Prior Arts
It is well known in the field that the ground is divided into the signal ground (hereafter called as SG) and the frame ground (hereafter called as FG), sometimes called as the chassis ground, to reduce the radiation noise. A Japanese patent application published as JP-2003-283177A has disclosed a noise reduction apparatus that provides one of such techniques, where the noise current to be sunk to the FG is reduced by dividing it into two portions and leading one of portions to the SG. This apparatus has a capacitor connected between the SG and the FG. Thus, the noise current is to be flowed from the FG to the SG through the capacitor. In other words, the impedance of the FG at high frequencies may be decreased by the capacitor between two grounds.
The capacitance of the capacitor is necessary to be a several pico-farad (pF) or greater in a range of several giga-hertz (GHz). While, the capacitor is also necessary to have a large isolation voltage at relatively low frequencies. The IEC standard rules that the capacitor used in such an application has an isolation voltage greater than 500 V. It is not practical that a capacitor is able to cope with both the high frequency performance and the large isolation voltage.
The present invention is to provide a technique to decrease the impedance between the FG and the SG as maintaining the isolation tolerance between the grounds without using any capacitor as a circuit component.